Provided is a synchronous motor assembly, comprising a motor , a motor driving circuit, and an adjusting unit which are in serial connection with two ends of an AC power supply. The motor driving circuit is used for driving the motor to run. Before the motor is started or during the starting and running process of the motor, the adjusting unit adjusts the motor to different stable voltage points so as to adjust the rotating speed of the motor. The invention is advantageous in that the synchronous motor assembly is simple in structure, stable in speed, and low in cost, and can drive the load toachieve wide-scope speed regulation; in the application of the blower fan and water pump, the rotating speed of fan blades or impellers can be adjusted through gearshift, so that user demand can be met.